Deep Renders (Exr 2.0)

Add support for rending deep files (exr 2.0 with deep samples) from Cycles.

Most production renders support this (mantra, karma, arnold, 3delight, redshift, prman, vray etc)

Its crazy powerful in comp, no need to holdouts or re-renders if small things in a renderlayer changes.

Reading material:

en.wikipedia.org/wiki/Deep_image_compositing

wetafx.co.nz/research-and-tech/technology/deep-compositing/

fxguide.com/featured/the-art-of-deep-compositing/

learn.foundry.com/nuke/8.0/content/user_guide/deep/deep_compositing.html